1. Field of the Invention
This application relates to a power transmission for a vehicle capable of operating on a snow surface.
2. Description of the Related Art
Snowmobiles are used for transport across snow surfaces, such as snowfields in cold climates. In a conventional snowmobile, an “endless” track belt (referred to herein as a track belt) is wrapped around front and rear wheels provided under the snowmobile vehicle body. The snowmobile is propelled as the track belt moves about the wheels, which are rotated by rotation of a power transmission connected to a drive shaft driven by an engine. One variation of the conventional snowmobile has front wheels with a sprocket that includes drive projections that engage driven projections and recesses on the track belt. The recesses are sometimes referred to herein as “windows.”
More particularly, this conventional snowmobile has a pair of rows of projections formed at constant intervals along the moving direction of the track belt that are formed on the left and right sides of the inside round surface of the track belt. Between the paired driven projections, driven windows extend through top and reverse surfaces of the track belt at constant intervals along the moving direction of the track belt. The conventional snowmobile includes left and right front wheels connected to the drive shaft that include a sprocket with projection drive portions and window drive portions. The projection drive portions are formed around the outer perimeter of the sprockets on lateral sides thereof and are configured to engage the driven projection on the track belt. The window drive portions are formed around the outer perimeter of the sprockets and are configured to engage the driven windows on the track belt.
In the conventional design, the snowmobile propelled forward when rotation of the drive shaft, which, when a transmission is engaged, causes driven projections and windows on the track belt to be engaged by the projection drive portion and window drive portions respectively. In some conventional belt designs, surfaces of the belt are clad with steel.
A problem with the conventional design, however, is that the impact between the drive and driven parts, e.g., between the window drive portions and the driven windows creates a lot of noise, particularly with the surface of impact of these components covered with steel. While removing the steel would reduce the impact noise, it also would decrease the durability or lifespan of the track belt.